1. Field of the Invention
The invention relates to an apparatus for adjusting an optical element in a lens system. More particularly the invention relates to a lens in a projection exposure objective for semiconductor lithography.
2. Description of the Related Art
In a projection exposure objective for manufacturing semiconductors, the optical elements, e.g. lenses, have to be adjusted extremely precisely. For the precise adjustment, it is also necessary to have manipulators or actuators which can displace the optical element in the xcexc-range and can tilt the optical element in the xcexcm-rad range.
For this purpose, DE 199 05 779 has already disclosed the practice of connecting the inner mount and outer mount of a lens to one another via elastic connecting members. Tilting positions of the optical element can be adjusted by adjusting elements with a plurality of connecting rods.
EP 1 035 426 A1 has likewise already described an apparatus for displacing an optical element, a retaining ring being connected to a supporting ring via elastic solid-state articulations.
The object of the present invention is to provide an apparatus of the type mentioned in the introduction in which, by means of highly precisely operating manipulators or actuators, it is possible to execute tilting of an optical element in the xcexcm-rad range and, if appropriate, displacements in the z-direction.
According to the invention, this object is achieved by an adjusting apparatus for an optical element in a lens system, for producing tilting movements, having at least one actuator, the optical element being connected via elastic connecting members, directly or indirectly via an inner mount, to an outer mount, wherein the elastic connecting members or the at least one actuator are/is provided in each case with bearing bridges which have bearing locations for a connection to the optical element, or the inner mount, and bridge arms which are connected to the bearing locations, said bridge arms being provided with piezoceramic elements in plate or sheet form which undergo changes in length upon activation, wherein said piezoceramic elements of the various bearing bridges are activatable, individually or together.
The optical element can be a lens in a projection exposure objective for semiconductor lithography.
The configuration according to the invention of the elastic connecting members and the actuation thereof via the highly responsive and very sensitive piezoceramic elements as actuators make it possible to execute tilting in the xcexcm-rad range. If all the piezoceramic elements are activated together, it is possible to execute z-displacements of the optical element in the xcexcm-range.
In the case of the adjustment according to the invention, use is made of the effect where piezoceramic elements change shape, in particular change in length, when they are activated electrically. If an appropriate voltage is applied to the piezoceramic elements, the bridge arms correspondingly bend or lengthen, which results in a lifting or lowering movement of the associated bearing location. Via the connection of the bearing location to the optical element, the latter is thus likewise raised or lowered. If this is not executed uniformly around the circumference at all the bearing locations, then individual lifting or lowering movements of the bearing locations result in the optical element tilting. With uniform and simultaneous activation of all the piezoceramic elements, displacement of the optical element in the z-direction takes place.
If the bridge arms are arranged in an inclined or oblique manner, then a more rigid attachment in the z-direction is achieved since force dissipation via the oblique bridge arms is possible as a result. With bridge arms which are horizontal or arranged transversely to the z-direction, in contrast, the result is a very low level of rigidity with corresponding isolation in relation to disruptive forces acting from the outside. In this case, however, it is necessary to take account of the correspondingly lower threshold in relation to natural frequencies.
A further advantageous configuration of the invention may consist in that the bearing locations are provided with recesses.
The recessing at the bearing locations makes it possible to achieve better isolation of disruptive movements which act from the outside.